The present invention relates to a serial reading type input scanning device.
Although various input scanners are conventionally known, typical examples are (1) a drum scanner, (2) a sensor array scanner, (3) a solid-state camera, and (4) a serial scanner. Therefore, these four types of scanners will be briefly described below.
(1) Drum Scanner:
In this scanner, paper to be read is adhered to a rotary drum, the drum is rotated, and a single reading sensor is slowly moved along the surface of the drum and parallel to a rotating shaft thereof, thereby reading an image. However, since an error between reading rows adversely affects every time the drum rotates, large units such as a drum must be manufactured with high accuracy, naturally resulting in high cost. In addition, a reading speed is low because a single sensor is used.
(2) Sensor Array Scanner:
In this scanner, optical reading sensors such as CCDs are arranged in a row direction, and a sheet of paper is continuously fed, thereby reading data of a sensor width at a time. This scanner is mainly used as a reading section of a facsimile device or the like and has many advantages in terms of operability (especially a reading speed). However, if a sensor width is increased, a problem of uniformity of sensors or reliability thereof (a single broken element leads to malfunction) is posed, resulting in a reduction in the yield and high cost.
(3) Solid-State Camera:
In this scanner, an image is projected onto sensors such as CCDs arranged in a matrix manner and electrically read in horizontal and vertical directions, thereby reading the image. This scanner is suitable for catching the entire image, but is not suitable for graphic reading (e.g. drawings) which requires high accuracy because of distortion of an image and inaccuracy caused by its structure.
(4) Serial Scanner:
In this scanner, sensing elements of one column move in a direction perpendicular to a feeding direction of paper to be read and sequentially read data, the paper is fed by one row after the one row is read, and after the paper is fed, the next row is then read. This scanner is not suitable for high accuracy reading such as graphic reading since a blank or an overlapped portion tends to be formed between read rows. In addition, since there are many movable portions, read data differs from source data in a large device.
The serial scanner has a simple mechanism as compared with the former three scanners but is more or less poor in accuracy.
On the other hand, a personal computer in recent years has been significantly improved in functions and widely used in a field of a work station of computer aided design (CAD). In addition, output devices, e.g., a printer and a plotter, have been significantly developed. However, input devices, e.g., a keyboard, a tablet, and a mouse, are still manually operated. Therefore, in order to automatically input information, strong demand has arisen for development of a low cost input scanner with high accuracy.